Thanks for the explanation So if a tablespace has 2 datafiles, one per array, and if a segment located in the tablespace spans in these two datafiles, can this segment have part of data in HCC and others parts not? Thanks! On Tue, Mar 20, 2012 at 6:29 PM, Tanel Poder <tanel@xxxxxxxxxxxxxx> wrote: > Oracle supports HCC on Exadata and from 11.2.0.3 onwards on Oracle's (Sum) > ZFS appliance and Pillar. Obviously on non-Exadata the *de*compression > always happens at the database layer (on Exadata it depends on a number of > things). The compression always happens in the database layer on both > Exadata and non-Exadata. > The HCC "support" is decided at the tablespace level, but HCC itself is > enabled at the segment level. So you can have a table residing in > HCC-capable tablespace, but you decide not to compress it. > > This segment-level approach also means that you can move the oldest > partitions of a partitioned fact table onto Pillar/ZFS appliance (and keep > it compressed with HCC if you want) while keeping the newest partitions of > the same table on Exadata storage. By the way, even with regular NFS > appliances or iSCSI storage you can keep some partitions of a table off > Exadata (without HCC) while keeping other partitions on Exadata. > > -- > *Tanel Poder* > Enkitec Europe > +372 56 956 181 > http://www.enkitec.com/ > Expert Oracle Exadata book: > http://www.apress.com/9781430233923 > > > > On Tue, Mar 20, 2012 at 4:13 PM, Vit Spinka <vit.spinka@xxxxxxxxxxxx> > wrote: > > > > > The HCC is usually done by the storage; if the storage decides not to do > > so (e.g. due to CPU load), it will pass the blocks uncompressed and it's > > then job of the database to uncompress them. So Oracle does not support > > HCC on non-Exadata/Pillar, but it could do so, but with performance hit. > > > > >> I am wondering because I am not very sure where is HCC done, if it is > > done > > >> in the DB how the hcc algorithm applies for some blocks (pillar) and > > some > > >> not (EVA), if it works shouldnt be a performance hit? > > >> > > > > > > > -- > > //www.freelists.org/webpage/oracle-l > > > > > > > > > -- > //www.freelists.org/webpage/oracle-l > > > -- //www.freelists.org/webpage/oracle-l